You wil automatically become a member after completing your first Disney Cruise. There is no fee to belong. Any past Disney cruiser is part of the group!
As said above, you become a member after your first cruise and it's absolutely free, the perks are in the future if you take another cruise, you have an express check-in line, and you get a gift in you're state room with the DCL logo (I think right now its a towel)
Tell your TA at Dreams that you are a past cruiser and they can have DCL look it up and add it to your reservation. You don't need your Castaway Club membership #, they can find you by name or phone number.
GET UP TO A $1000 SHIPBOARD CREDIT AND AN EXCLUSIVE GIFT!
If you make your Disney Cruise Line reservation with Dreams Unlimited Travel you’ll receive these incredible shipboard credits to spend on your cruise!